Reactor for treating liquids

ABSTRACT

A reactor for removing impurities by electrochemcial means from liquids, such as aqueous solutions, and in which the liquid is passed through series of plateshaped reaction electrodes electrically insulated against each other with a liquid speed above a minimum to prevent dissociation into constituent gases, but sufficient to ensure interaction with an electrical current passing between the plateshaped electrodes. The latter has corrugated forms and/or their surfaces provided with embossed relief patterns to enhance the electrochemical effect between the electrodes. The reactor comprises one more interconnected units (A, B, C, D) with a series of plateshaped electrodes ( 1, 2 ) valve means ( 8 ) and holes ( 5, 6 ) in the plates for redirecting the liquid flow into and through the series of reaction electrodes ( 1, 2 ). An control system consists of a number of sensors ( 9, 10, 11 ) at the liquid inlet ( 3 ) of the reactor for measuring the conductivity of the treated liquid, the organic contents of the liquid and the flow of the liquid means ( 9′, 10′, 11′ ) for transferring the measurements to a processor ( 7 ) for further treatment, and means ( 13, 14, 15 ) for transferring the output commands from the processor ( 7 ) to the valve means ( 8 ) for redirecting the liquid flow and for activating or deactivating the electrode unit or units (A, B, C, D) in dependence on the measured parameters.

[0001] The invention relates to a reactor for treating liquids with aview to remove impurities by electrochemical means.

[0002] Liquids such as waste water have traditionally been cleaned bymeans of chemical and biological treatment and sedimentation. Oxidationis performed in aerators, and micro-organisms will deal with nutrientsalts as well as with heavy metal ions. These processes are notdifficult to perform but they require large plants and considerableprocess time. Hence they are frequently performed on waste water and noton fresh water pumped up for consumption or on surface water. For wastewater it has become standard practice to perform membrane filtration,for example in the form of reverse osmosis for salt removal and microfiltration for removal of micro-organisms. Sometimes chlorination,UV-radiation and ozonification is used. Such plants are, however, verycomplex, and their working pressures have to be large which puts heavyrequirements on the pumps involved. Hitherto known purifying plants arenormally constructed according to the removal of specific impurities,and modifications to perform optimally for other impurities, which mayappear, are complex and time consuming.

[0003] Production enterprises have today to pay for the degree ofpollution of their effluents which often represents a significantexpense in production operation and involve the costs of theinstallation of large purification facilities within the productionplant in question.

[0004] There is hence a hitherto unfilled need for an apparatus orreactor which is easily adaptable to changing purifying requirements andwhich does not require large plants of very high operating pressures.

[0005] It is known that electrochemical processes may have a biocidaleffect on the bacteria content in a treated liquid due to the electricalcurrent. It is also well known to produce a mechanical, catalytic andmagnetic stimulation of the oxidation/reduction processes of organicsubstances in waste water. By using a reactor with a heterogeneouselectro-chemical action it is feasible to solve the problems outlinedabove. However, existing equipment which is available forelectrochemical processes is designed for the synthesis of organic ormetallo-organic compounds and is not well suited for treating largevolume flows of liquid, such as waste water. Mere re-configuration ofequipment of the known type to achieve this aim has not hitherto provedeconomical.

[0006] It is therefore a purpose invention to provide an apparatus orreactor which is well suited to the purifying processes envisaged andwhich is adaptable to a wide range of flows and effluent parameters andin which it is simple to provide further specific functionalities forexisting purifying plants.

[0007] This is obtained by means of a reactor according to the inventionin a process in which the liquid, such an aqueous solution, is passedbetween a series of plateshaped, corrugated reaction electrodes with avolume speed which is above a minimum to prevent dissociation intoconstituent gases but sufficient to ensure interaction with anelectrical current passing between the reaction electrodes, which areelectrically insulated against each other, the reactor being particularin that it comprises at least one and preferably more interconnectedunits with series of plateshaped electrodes, valve means and holes inthe plates for redirecting the liquid flow into and through the seriesof reaction electrodes, and an automatic electronic control systemconsisting of a number of sensors at the liquid inlet of the reactor formeasuring the conductivity of the treated liquid, the organic contentsof the liquid and the flow (volume) of the liquid, means fortransferring the measurements to a processor for further treatment, andmeans for transferring the output commands from the processor to thevalve means for redirecting the liquid flow and for activating ordeactivating the electrode unit or units in dependence on the measuredparameters.

[0008] To enable simple, fast and efficient changes in the passing flowwhile using standardized electrode plates, a preferred embodiment of theinvention is particular in that the electrical insulation between theplates is shaped as liquid tightening gasket sealings acting asmanifolds and flow controllers. A further embodiment is particular inthat the processor also includes means for adjusting the density of theelectrical current passing between the plates.

[0009] Another advantageous embodiment in particular is that at leastsome electrode surfaces are coated with layers of catalytic compoundsincluding pure metals.

[0010] In a further advantageous embodiment the electro-chemical processplates are interspersed with heat exchanger plates to obtain a bettertemperature control of the process and to recover the heat from thetreated liquid.

[0011] Yet another advantageous embodiment comprises the placement ofseparation membranes between one or more electrode pairs.

[0012] In a further advantageous embodiment specially shapedelectromagnets are connected with some of the plateshaped electrodes toprovide a magnetic field in the space between an electrode pair and thusstimulate the process between the plates.

[0013] In a further advantageous embodiment ultrasonic actuating devicesare fitted into the manifolds of the single units to likewise stimulatethe process between the plates of the unit in question therebyincreasing the efficiency of the process. Gases are formed by theelectro-chemical reaction between electrodes and if the gases areallowed to accumulate they get larger and larger with the result, thatthe gases generated to work in the process gets lost to the solution. Byusing ultrasound the gas bubbles are stimulated to expand and thenimplode, whereby the gases are returned to the solution. An additionaladvantage in this connection is a cleaning effect upon the electrodesduring the process.

[0014] All the above embodiments allow for the inclusion of the reactorinto existing heat exchanger installations of purifying systems forwaste water in order to pre-process the effluent before it is lead intosewage systems, and due to its modest outer dimensions and simpleconstruction principals the reactor provides thus a surprising new meansfor purifying of effluents.

[0015] The invention will be further described in the following withreference to the accompanying drawings, in

[0016]FIG. 1 schematically shows the built-up of a unit of plateshapedelectrochemical reaction electrodes with a lower liquid and an upperliquid outlet;

[0017]FIG. 2 shows a pair of plateshaped electrodes seen from the backand from the front, respectively;

[0018]FIG. 3 shows schematically the relative positioning of two cathodeplates above and below with a anode plate in between, all three platesbeing corrugated, and the appertaining process passages between theplates;

[0019]FIG. 4 shows a cross section of the placement of liquid sealingand electrically insulating gaskets between the plates;

[0020]FIG. 5 shows diagrammatically and partly in an exploded view areactor according to the invention comprising four interconnected unitseach with a number of plateshaped electrodes, valve means and aprocessor the automatic control of the reactor;

[0021]FIG. 6 shows diagrammatically and in cross section two examples ofthe positioning of the valve means;

[0022]FIG. 7 shows schematically the built-up of the electrode plates ina unit with interspersed heat exchanger plates;

[0023]FIG. 8 shows schematically the positioning of membranes betweenthe electrode plates in a unit;

[0024]FIG. 9 shows schematically the fitting of an electromagnet to anelectrode plate; and

[0025]FIG. 10 shows also schematically an ultrasound device and itspositioning in a liquid passage way through a unit.

[0026] In FIG. 1 is shown the principle of the built-up of a unit of thereactor according to the invention, the unit comprising a number ofplateshaped electrodes in the form of cathodes 1 with anodes 2 betweenthe cathodes, a lower liquid inlet 3 and an upper liquid outlet 4. Itwill be seen from the figure that the unit built-up is very much alikethe traditional construction of a plate heat exchanger, however, withthe difference that the unit electrode plates advantageously arehorizontally placed contrary to heat exchanger plates, which more oftenare vertically placed. This horizontal positioning of the electrodeplates with lower liquid inlet 3 and the upper liquid outlet 4 is due tothe fact that air bubbles occurring in the treated liquid in the reactorshould be allowed to pass out of the system in a ‘natural’ way insteadof harassing the purifying process. Tie rods (not shown) hold the stackof plates together between end plates to form the unit in the same wayas in the construction of a plate heat exchanger.

[0027] In FIG. 2 are shown two consecutive electrode plates 1 (lowersurface) and 2 (upper surface). Ordinarily the plates have holes 5, 6near each corner. With the plates mounted in a stack the holes representa longitudinal flow passage through the stack or the unit and of alength which is equal to the height of the stack. Close to the peripheryof each plate 1, 2 and around the holes 6 is a grove 20 in the uppersurface of a plate for holding a liquid tightening and electricallyinsulating gasket 19 (cf. FIG. 4) and a corresponding rim 20 a on thelower surface of the plate. When stacking the plates to form a unit andtight the tie folds the gaskets 19 in the groves 20 will press againstthe raised rims 20 a upon the lower surfaces of the plates immediatelyabove and be compressed to a liquid tightening seal. This constructionensures also that the edge effect (concentration of electricalpotential) associated with electrode plates in an electrolyte isavoided, because the liquid is confined within the outer gaskets andeliminates thus a source of undesired process activity.

[0028] Ordinarily the plates have holes 5, 6 near each corner. A stackof holes represent a longitudinal flow passage of a length equal to theheight of the stack which allows access to each space between adjacentplates 1, 2. However, if a gasket 19 surrounds a hole 5 the access fromthe flow passage into a space around the gasket is blocked, and the flowin that particular flow passage bypasses the space. The flow passageformed by the gasket blocked holes 5 is now acting as a manifold. InFIG. 2 a liquid flow in the space between the electrode plates 1 and 2is therefore fully determined by the access holes 6 which act as sourceand drain or vice versa.

[0029] In FIG. 3 is schematically shown that the plates 1, 2 arepreferentially corrugated to enhance a turbulence which will cause aconstant and better mixing of the liquid mass during its transportbetween the plates. The plate surfaces may also be provided with theembossed relief patterns. This embodiment of the plates causes thepassing liquid mass to be continuously moved into the ‘clouds’ ofsolvated electrons, radicals and ions associated with the respectiveelectrodes. Furthermore, the process active area of each plate 1, 2 isincreased by this embodiment of the plates. It also appears from thisfigure that a series of plateshaped electrodes comprises alternatinglymounted cathodes 1 and anodes 2, each plate being connected to anelectrical source (now shown).

[0030]FIG. 4 shows schematically and on enlarged scale a cross sectionof the fitting of sealing gaskets 19 in the respective plates 1, 2. Thegaskets 19 are cemented in place in the groves 20 of the plates 1, 2before assembling a stack of plates. When the stack hence is assembledby tightening the tie rods of the stack or unit the upper part of eachgasket 19 is brought to rest against the rim 20 a on the back surface ofeach foregoing plate and fixed by the compression caused by thetightening.

[0031]FIG. 5 shows diagrammatically and partly in an exploded view apreferred embodiment of the reactor according to the invention, thereactor comprising four interconnected units or stacks A, B, C, D ofplate shaped electrodes 1, 2 mounted alternatingly in pairs of cathodes1 and anodes 2, a reactor liquid inlet 3, a reactor liquid outlet 18 andeach unit A, B, C, D having liquid flow passages 6 with access to thespaces between the plates and blocked liquid flow passages 5 acting asmanifolds for bypassing liquid through the respective units. Theelectrode plates are provided with connections 16, 17 to a not shownelectrical source. Immediately below each unit is mounted automaticallycontrolled valve means 8 of a known construction for directing andredirecting the flows through the units A, B, C, D. The reactorcomprises further a processor 7 connected by means 9′, 10′, 11′ tosensors 9, 10, 11 mounted on the reactor inlet 3 for measuring theconductivity of the liquid fed to the reactor, the organic contents ofthe liquid and the flow (volume) of the liquid. After treatment of themeasured parameters in the processor 7 the output data are sent throughmeans 12, 13, 14, 15 as commands from the processor to the valve means 8to direct and/or redirect the liquid flow through the units A, B, C, Din dependence on the measured parameters.

[0032] The processor 7 may include means (not shown) for the adjustmentof the electrical current passing between the pairs of electrodes.

[0033] The electrode surfaces may be coated with various types ofcatalytic compounds including pure metals according to the substances itis desired to remove from the effluents. As appropriate coatingmaterials thin layers of stainless steel, graphite, platinum and leaddioxide may be used.

[0034]FIG. 6 shows in simplified diagrams the valve means principlewithin a stack or unit A, B, C, D of electrode plates 1, 2 (cf FIG. 5).As indicated in the right side of the FIGS. 6a and 6 b the plates 1, 2are cathodes (−) and anodes (+). The sealing and insulating gaskets 19are shown at the ends of the plates 1, 2 and prevent any liquid flowsaround the plate ends. Valves 18 a-18 h are mounted in the liquidpassages 6 which give liquid access to the spaces between the plates.The valves 18 a-18 h are controlled mechanically, electrically orhydraulically in a known manner via the valve body 8 immediately beneatheach unit A, B, C, D, the body 8 receiving its electronic commands fromthe processor 7 (cf. FIG. 5). Two different valve positions are shown.In FIG. 6a the liquid enters via the inlet 3 and travels through passage6 the entire depth of the stack. As the left passage is blocked at thetop by valve 18 a and as the parallel passage 6 at the right on thefigure is blocked at the bottom by valve 18 h and the remainder valves18 b-18 g are all open the entire liquid mass moves horizontally fromleft passage 6 to right passage 6 and exits via outlet 4 above the rightpassage 6. The unit has full liquid flow, but a given mass of liquidpasses only once between a cathode/anode pair.

[0035] In FIG. 6b all valves 18 b-18 h are closed and only valve 18 a inleft passage 6 is open. Hence the liquid flow entering through inlet 3is constantly redirected by the valves during its passage of the unit,so that a given mass of liquid passes between cathode/anode pairs 1, 2six times. The treating effect of this unit is therefore here six timesas great as the treating effect in the foregoing example, but the flowis inversely proportional.

[0036]FIG. 7 shows a stack of electrode plates with cathodes 1, 1 a, 1b, 1 c, 1 d alternating with anodes 2, 2 a, 2 b, 2 c, where heatexchanger plates 21 and 21 a are interspersed between electrode pairs 2a-1 b and 2 b-1 c, respectively, to obtain a better temperature controlof the process between the plates and to recover heat from the processfor further use within the plant of which the reactor according to theinvention is part.

[0037]FIG. 8 shows a stack of electrodes 1, 2 in which membranes 22 arefitted between the electrode pairs. As membranes may be usedsemi-permeable membranes known per se for the separation of moleculesand ions in liquid form or as gas from the process. The latter will inmany cases liberate gases and the creation of a vacuum occurring above amembrane connected to a particular electrode may remove the gasesproduced. Membranes may also be used to only allow for the transport ofelectrons and specific ions through the space between an electrode pairaccording to any special requirements for the purifying process.

[0038]FIG. 9 shows a configuration of an electrode 1 adapted formagnetic stimulation of the processes taking place on either side of theelectrode. Pole pieces 23, 24 of magnetically conductive material, suchas transformer laminations, and with appertaining windings (not shown)form an electromagnet fitted to the edges of the electrode plate 1 madeof magnetic material such as certain types of stainless steel. Whenactivating the electromagnet 23, 24 in a known manner a magnetic fieldis created in the process space between an electrode pair and willstimulate the reaction process.

[0039]FIG. 10 shows an ultrasonic device for ultrasonic stimulation ofthe processes within a reactor unit A, B, C, D. With 26 is indicated alongitudinal flow passage formed by the holes 6 (cf. FIG. 5) through astack of electrode plates or unit and with access to the spaces betweenthe electrode pairs. The flow passage is provided with inlet 27 andoutlet 28 pipes for feed or drain of treated liquid. A ultrasonictransducer 25 mounted on a rod 29 is fitted into the longitudinal flowpassage, the length of the rod 29 corresponding to the height of thestack in which the desired stimulation should occur. When activating thetransducer 25 ultrasound is spread due to the low losses and highvelocity of sound in the treated liquids through the flow passage 26 andfrom the latter out in to the reaction spaces between the electrodesthus stimulating the process in these spaces. The rod-shaped ultrasonicdevice 25, 29 is of a size which will allow for passage of liquidthrough pipes 26, 27, 28 even with the device in mounted position.

[0040] Below is given a simple example of the functioning of the reactoraccording to the invention and with reference especially to FIG. 5.Provided that the four units A, B, C, D are of equal size and eachcontain 13 electrode reaction spaces, each space being passed by 400ml/h treated liquid, the flow through each unit is 5.2 L/h and hence theflow through four units is 20.8 L/h in case the four units all workparallel and with the same flow direction. This gives a maximum flow anda minimum physical effect. If the liquid passes in parallel flows and inthe same direction through the two lowermost units A, B and then isredirected to pass still in parallel flows, but in the oppositedirection through the two uppermost units C, D, the passing liquid massis reduced by ½, i.e. 10.4 L/h, but the effect is doubled. There arethen two parallel and two serial unit flows.

[0041] If the liquid flow is passed consecutively and parallely throughall four, serially connected units and redirected when passing from oneunit to the next following one, which means that the flow passes in thesame direction through units A and C and in the opposite directionthrough units B and D the flow rate of the reactor will be minimum, i.e.that of a single unit of 5.2 L/h, but as the flow passes four timesthrough identical spaces the corresponding effect will be maximum.

[0042] In addition to the adjustments of effect due to flow, theadjustments of electrical current density is varied to the desired levelby means of the processor. If the physical flow of liquid fed to thereactor is reduced and thus require less processing without changing theneeded effect, the liquid volume can simply be reduced to the levelneeded by exiting the treated liquid through outlets (not shown) in thevalve means corresponding to the liquid mass.

[0043] From the above it should be understood that the reactor accordingto the invention represents an extremely versatile apparatus whichwithout undue experimentation is adaptable to any desired liquidpurifying process based upon basic principals.

1. A reactor for removing impurities by electrochemical means fromliquids, such as aqueous solutions, and in which the liquid is passedthrough series of plateshaped reaction electrodes electrically insulatedagainst each other with a liquid speed above a minimum to preventdissociation into constituent gases, but sufficient to ensureinteraction with an electrical current passing between the plateshapedelectrodes, the latter having corrugated forms and/or their surfacesbeing provided with embossed relief patterns to enhance theelectrochemical effect between the electrodes, the reactor comprisingone or more interconnected units (A, B, C, D) with series of plateshapedelectrodes (1, 2) valve means (8) and holes (5, 6) in the plates forredirecting the liquid flow into and through the series of reactionelectrodes (1, 2) and a control system consisting of a number of sensors(9, 10, 11) at the liquid inlet (3) of the reactor for measuring theconductivity of the treated liquid, the organic contents of the liquidand the flow of the liquid means (9′, 10′, 11′) for transferring themeasurements to a processor (7) for further treatment, means (13, 14,15) for transferring the output commands from the processor (7) to thevalve means (8) for redirecting the liquid flow and for activating ordeactivating the electrode unit or units (A, B, C, D) in dependence onthe measured parameters.
 2. A reactor according to claim 1, in which theseries of plateshaped reaction electrodes comprise electrolytic processplates of alternatingly mounted anode (1) and cathode (2) plates eachconnected (16, 17) to an electrical source.
 3. A reactor according toclaim 1 or 2, and in which the electrical insulation between adjacentelectrode plates (1, 2) comprises electrically insulating and liquidtightening gasket sealings (19) mounted in groves (20) along theperimeter of the plateshaped electrodes (1, 2) and round part of theholes (5) in the same and shaped in such a way that the gaskets (19) actas manifolds and flow controllers of the liquid passing through theseries of electrodes (1, 2).
 4. A reactor according to claim 1, in whichthe processor (7) also includes means to adjust the density of theelectrical current passing between the reaction electrodes (1, 2).
 5. Areactor according to any of claims 1 to 3, in which at least some of thesurfaces of the electrolytic process plates (1, 2) are coated withcatalytic compounds including pure metals.
 6. A reactor according to anyof claims 1 to 3 or 5, in which the electrolytic process plates (1, 2)are interspersed with heat exchanger plates (21) for heat recovery fromthe treated liquid.
 7. A reactor according to anyone of the foregoingclaims, in which separation membranes (22) for separating molecules andions in liquid form or gas from the treated liquid are mounted betweeninteracting pairs of electrodes (1, 2).
 8. A reactor according to any ofclaims 1 to 3, in which electromagnetic devices (23, 24) are fitted to anumber of electrolytic process plates (1, 2) being made of magneticmaterial to create a magnetic field around a process plate forstimulating the reaction process taking place on either side of theplate (1, 2).
 9. A reactor according to claim 1 or 2, in which anultrasonic device (25, 29) is fitted into the longitudinal liquidpassage way (26) through a series of electrolytic process plates (1, 2)to generate ultrasound in the longitudinal passage (26) for stimulationof the reaction process between the plates of the series.